Controller for data recorder

ABSTRACT

A controller for a data recorder controls data recording to prevent buffer overrun errors. The data recorder emits a laser beam against a recording medium to record data. The data has a level that determines the power of the laser beam. When there is a possibility of a buffer overrun, the controller interrupts data recording. The controller interrupts data recording when the power of the laser beam is a low level and restarts data recording with the laser beam generated at the low level.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a divisional and claims the benefit ofpriority under 35 USC 120 of pending U.S. application Ser. No.09/717,771, filed Nov. 21, 2000, which claims the benefit of foreignpriority under 35 USC 119 of Japanese applications 11-331419, filed Nov.22, 1999 and 2000-322550, filed Oct. 23, 2000. The disclosure of theprior applications is considered part of and is incorporated byreference in the disclosure of this application.

FIELD OF THE INVENTION

[0002] The present invention relates to a data recorder, and moreparticularly, to a controller for a data recorder having a buffer memoryfor storing data provided from an external device and recording thestored data of the buffer memory on a recording medium.

BACKGROUND OF THE INVENTION

[0003] An optical disc recorder records data on an optical disc, whichserves as a recording medium. A CD-DA family compact disc-recordable(CD-R) drive is one type of optical disc recorder that is widely used. ACD-R is a so-called write-once optical disc on which data is writtenonly once. The recorded data cannot be physically deleted. A laser beamis irradiated against the optical disc from an optical head of the CD-Rdrive. The heat of the leaser beam melts a dye and forms recording pitson a recording layer of the optical disc. Data is recorded on the discby changing the reflecting rate of the recording layer.

[0004] The optical disc recorder includes a buffer memory and anencoder. The buffer memory temporarily stores data provided from anexternal device, such as a personal computer. The encoder reads the datafrom the buffer memory and encodes the read data to record the data onthe optical disc.

[0005] In such an optical disc recorder, if, for example, the rate ofdata transmission from the external device is slower than the recordingdata transmission rate of the optical disc (write speed), thetransmission rate of the recording data output from the encoder isfaster than the transmission rate of the data provided to the buffer.This decreases the amount of the data stored in the buffer memory. Ifthe decrease continues, the data amount ultimately becomes null and thebuffer memory becomes empty. This stops the stream of data to theencoder and causes an interruption in the data recorded on the opticaldisc. This problem is referred to as buffer underrun. The interruptionin the data recorded on the optical disc resulting from buffer underrunis referred to as a buffer underrun error.

[0006] Data is recorded on an optical disc using a recording techniquethat designates the file group recorded on the optical disc (e.g., discat once, track at once). Thus, if a buffer underrun error occurs, theentire optical disc becomes unusable when employing disc at once, andthe track undergoing recording becomes unusable when employing track atonce.

[0007] Recent CD-R drives record data at a speed four times or eighttimes the normal recording speed. Further, recent personal computershave multitasking functions to operate CD-R drives. This has increasedthe tendency of the occurrence of buffer underrun errors.

[0008] Packet writing is one type of data recording that records data inpacket units. Packet writing records data on an optical disc when thedata reaches the capacity of the packet. This prevents the occurrence ofbuffer underrun errors. However, the link blocks must be formed toconnect packets in packet writing. The link blocks decrease therecording capacity of the optical disc. Further, there are CD-ROM drivesthat are not capable of handling packet writing. Such CD-ROM drivescannot reproduce data written to optical discs through packet writing.In other words, the CD-ROM compatibility required by the CD-R standard(Orange Book Part II) does not include packet writing. For example,packet writing cannot be applied for a CD-DA player. Thus, a CD-R drivecannot record CD-DA audio data through packet writing. Accordingly,there is a need for preventing buffer underrun errors without employingpacket writing.

[0009] A CD-rewritable (CD-RW) drive is another type of optical discrecorder that is widely used. A CD-RW drive irradiates a laser beam froman optical head against an optical disc. The heat of the laser beamcauses phase changes between amorphic and crystalline to form recordingpits on the recording layer of the optical disc. Data can be repeatedlyrewritten to optical discs used by the CD-RW drive. Accordingly, theoptical disc remains usable even if a buffer underrun error occurs.However, when a buffer underrun error occurs, the data file that wasbeing recorded before the occurrence of the buffer underrun error mustbe recorded again. This wastes the recording performed prior to theoccurrence of the buffer underrun error and increases the recordingtime.

[0010] A magneto-optic disc recorded is another type of known datarecorder. The magneto-optic disc recorder irradiates a laser beam froman optical head against a magneto-optic disc. This applies residualmagnetization to the recording layer of the optical disc and recordsdata on the magneto-optic disc. Mini disc (MD) drives are widely usedmagneto-optic disc recorders. However, MD drives have the same problemas CD-RW drives.

SUMMARY OF THE INVENTION

[0011] It is an object of the present invention to provide a controllerfor a data recorder that controls data recording in a manner that thecontinuity of the data is ensured even if the recording of data to arecording medium is interrupted.

[0012] To achieve the above object, the present invention provides acontrol circuit of a data recorder, which records data on a recordingdata by emitting a laser beam against a recording medium. The controlcircuit includes an interrupt control circuit for interrupting datarecording when a predetermined state is detected. The interruptionoccurs when the laser beam is generated at a relatively low power level.

[0013] A further respect of the present invention provides a controlleremployed in a data recorder to control interruption and restart ofrecording data. The data recorder records on a recording medium datastored in a buffer memory by repetitively emitting a laser beam againstthe recording medium. The laser beam is generated at a high level and alow level. The controller includes an address memory for storing atleast one of an address of the recording medium and an address of thebuffer memory when data recording on the recording medium isinterrupted. Each address indicates a location of data when therecording interruption occurred. A synchronizing circuit sequentiallyreads the data recorded on the recording medium prior to the recordinginterruption and the data stored in the buffer memory prior to therecording interruption while synchronizing the recorded data and thestored data. A restart circuit restarts data recording on the recordingmedium based on the address stored in the address memory. The controllerinterrupts data recording when the laser beam is generated at arelatively low power level.

[0014] Another aspect of the present invention provides a controlcircuit of a data recorder. The data recorder records data on arecording medium by emitting a laser beam against the recording medium.The data is formed by a plurality of sectors. Each of the sectorsincludes a synch pattern that has a predetermined number of bitsrepresenting a low level. The laser beam is generated at a low powerlevel in accordance with the low level of the synch pattern. Thecontroller includes an interrupt control circuit for continuingrecording until an interval between sectors appears when detecting apredetermined state and interrupting the recording operation when thelaser beam is generated in accordance with the synch pattern of asector.

[0015] Another aspect of the present invention provides a method forinterrupting data recording in a data recorder. The data recorderrecords data on a recording medium by emitting a laser beam against therecording medium. The data is formed by a plurality of sectors. Each ofthe sectors includes a synch pattern that has a predetermined number ofbits representing a low level. The laser beam is generated at a lowlevel in accordance with the low level of the synch pattern. The methodincludes continuing recording until an interval between sectors appearswhen a predetermined state is detected, and interrupting the recordingoperation when the laser beam is generated in accordance with the synchpattern of a sector.

[0016] A further aspect of the present invention provides a method forinterrupting and restarting data recording in a data recorder. The datarecorder records on a recording medium data stored in a buffer memory byemitting a laser beam against the recording medium. The method includesinterrupting data recording when a predetermined state is detected,storing in an address memory at least one of an address of the recordingmedium and an address of the buffer memory when data recording on therecording medium is interrupted. Each address indicates a location ofdata when the recording interruption occurred. The method furtherincludes sequentially reading the data recorded on the recording mediumprior to the recording interruption, synchronizing the recorded data andthe stored data, and restarting data recording on the recording mediumbased on the address stored in the address memory. The interrupting ofthe data recording is performed when the laser beam is generated at arelatively low power level.

[0017] Other aspects and advantages of the present invention will becomeapparent from the following description, taken in conjunction with theaccompanying drawings, illustrating by way of example the principles ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The invention, together with objects and advantages thereof, maybest be understood by reference to the following description of thepresently preferred embodiments together with the accompanying drawingsin which:

[0019]FIG. 1 is a schematic block diagram showing a CD-R drive accordingto a preferred embodiment of the present invention;

[0020]FIG. 2(a) is a schematic diagram showing a sector of an opticaldisc; and

[0021]FIG. 2(b) is a diagram illustrating addresses of a buffer memoryof the CD-R drive of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0022] With reference to FIG. 1, a CD-R drive 1 includes a spindle motor2, a spindle servo circuit 3, an optical head 4, and RF amplifier 5, ahead servo circuit 6, a decoder 7, a subcode decoding circuit 6, adecoder 7, a subcode decoding circuit 8, a wobble decoder 9, and ATIPdecoding circuit 10, and external connection terminal 11, an interface12, a buffer memory 13, an encoder 14, an encoder internal RAM 15, alaser drive circuit 16, a crystal oscillation circuit 18, an accesscontrol circuit 19, a buffer underrun determination circuit 20, arecording control circuit 21, and a system control circuit 22. The CD-Rdrive 1 is connected to a personal computer 31 via the externalconnection terminal 11 to record data, which is provided from thepersonal computer 31, on an optical disc 32 that complies with the CD-Rstandards. Further, the CD-R drive 1 provides the personal computer 31with data reproduced from the optical disc 32.

[0023] The spindle motor 2 rotates the optical disc 32. The spindleservo control circuit 3 controls the spindle motor 2 so that the opticaldisc 32 is rotated using the constant linear velocity (CLV) method inaccordance with the rotation control signal generated by the wobbledecoder 9.

[0024] When reading data, the optical head 4 irradiates a relativelyweak laser beam against the optical disc and, from the reflected laserbeam, generates a RF signal (high frequency signal) in correspondencewith the data recorded on the optical disc. When recording data, theoptical head 4 irradiates a relatively intense laser beam (several tensof times greater than the data reading laser beam) against the opticalbeam 32 to form recording pits on the recording layer to record data. Insynchronism, with the recording of data, the optical head 4 generatesthe RF signal in correspondence with the recorded data from thereflected laser beam.

[0025] The RF amplifier 5 amplifies the RF signal, which is providedfrom the optical head 4, and digitizes the amplified RF signal togenerate a digital data signal. The RF signal of the optical head 4 isfed back to the head servo circuit 6 via the RF amplifier 5. The headservo circuit 6 uses the RF signal to perform focusing control, trackingcontrol, and sled feed control. Focusing control focuses the laser beamon the recording layer of the optical disc 32. Tracking control tracksthe laser beam along a signal track of the optical disc 32. Sled feedcontrol moves the optical head 4 in the radial direction of the opticaldisc 32.

[0026] The decoder 7 decodes the digital data provided from the RFamplifier 5. Further, the decoder 7 generates a pit clock from thedigital data and separates a subcode from the digital data to generate asubcode synchronizing signal.

[0027] The subcode decoding circuit 8, which is incorporated in thedecoder 7, decodes the subcode. Further, the subcode decoding circuit 8generates subcode Q channel data (hereafter referred to a sub-Q data)from the decoded subcode.

[0028] The wobble decoder 9 extracts a wobble component of 22.05 kHzfrom a pre-groove signal of the optical disc 32 that is included in thedigital data provided from the RF amplifier 5. Then, the wobble decodergenerates the rotation control signal of the optical disc 32 from thewobble component.

[0029] The ATIP decoding circuit 10, which is incorporated in the wobbledecoder 9, uses the wobble component to decode an absolute time inpre-groove (ATIP) and extract absolute time information, or an ATIPaddress, from the ATIP. The absolute time information indicatesaddresses of locations in the recording medium.

[0030] The interface 12 controls data transmission between the personalcomputer 31 and the CD-R drive 1.

[0031] The buffer memory 13 is a ring buffer that includes a synchronousdynamic random access memory (SDRAM), which preferably has a FIFOconfiguration, and the buffer memory 13 stores data provided from thepersonal computer 31 via the interface 12. Data stored at one address ofthe buffer memory 13 corresponds to data recorded at one sector of theoptical disc 32.

[0032] An interrupt/restart circuit 43 of the system control circuit 22controls the encoder 14. The encoder 14 reads the data stored in thebuffer memory 13 in sector units and encodes the data into recordingdata for the optical disc 32. The RAM 15, which is incorporated in theencoder 14, stores the necessary data for encoding by the encoder 14 andintermediate operation encoding data. When performing data encoding incompliance with the CD-Rom standard, the encoder 14 adds a synch byte, aheader, a CD-ROM data error detection code (EDC), and an errorcorrection code (ECC) to the data. The encoder 14 further performs errorcorrection using a cross interleaved Reed-Solomon code (CIRC), which isa CD error correction code, and eight to fourteen modulation (EFM) onthe data. Further, the encoder 14 adds a subcode, which includes thesub-Q data, and a synchronizing signal of the subcode to the data.

[0033] The interrupt/restart circuit 43 also controls the laser drivecircuit 16, which provides a laser drive signal to the laser beam sourceof the optical head 4. The voltage of the drive signal is constant whenreproducing data and varied in accordance with the recording data outputfrom the encoder 14 when recording data. When the recording data outputfrom the encoder 14 is low (L), recording pits are not formed on therecording layer of the optical disc 32. Thus, the drive signal is set sothat its voltage is the same as when data is reproduced. When therecording data is high (H), recording pits are formed on the recordinglayer of the optical disc 32. Thus, although the voltage of the drivesignal differs between track positions, the drive signal is set so thatits voltage is several tens of times greater than during datareproduction.

[0034] The crystal oscillation circuit 18 generates an oscillationsignal based on the oscillation of a crystal oscillator.

[0035] The access control circuit 19 selectively refers to the subcodeaddress of the absolute time information in the sub-Q data and the ATIPaddress of the absolute time information in the ATIP to control therecording control circuit 21 and the head servo circuit 6. This controlsaccess to the optical disc 32.

[0036] The data provided to the buffer memory 13 is stored in the buffermemory 13 in a predetermined address order. The buffer underrundetermination circuit 20 directly or indirectly determines the amount ofdata stored in the buffer memory 13 from the address at which writing orreading is presently performed. Based on the data amount, the bufferunderrun determination circuit 20 determines whether or not the buffermemory 13 is in a state in which buffer underrun may occur.

[0037] Based on the determination result of the buffer underrundetermination circuit 20 and in response to a command provided from thepersonal computer 31, the recording control circuit 21 controls theinterface 12, the access control circuit 19, and the system controlcircuit 22.

[0038] The system control circuit 22 includes a system clock generationcircuit 41, a signal synchronizing circuit 42, the interrupt/restartcircuit 43, a retry determination circuit 44, location detectioncircuits 45, 46, and address memories 47, 48. These circuits 41-48 arelaid out on the same chip of an LSI substrate.

[0039] The system clock generation circuit 41 generates from theoscillation signal of the crystal oscillation circuit 18 a referenceclock used when recording data. Further, the generation circuit 41 usesa pit clock extracted by the decoder 7 to generate a reproduction clockused when reproducing data. The generation circuit 41 selects thereference clock or the reproduction clock in accordance with theswitching control performed by the signal synchronizing circuit 42. Theselected clock is sued as a system operational clock of the CD-R drive1. In accordance with the operational clock, the CD-R drive 1 controlsthe synchronization of the circuits 7-10, 12-16, and 19-22.

[0040] In accordance with the synchronizing signal of the subcode fromthe decoder 7 and the sub-Q data from the subcode decoding circuit 8,the signal synchronizing circuit 42 controls the recording controlcircuit 21 so that the recording data output from the encoder 14 issynchronized with the data recorded on the optical disc 32. Whenperforming this control, the sub-Q data of the subcode decoding circuit8 is associated with the sub-Q data of the encoder 14 aftersynchronizing the subcode synchronizing signal of the decoder 7 with thesubcode synchronizing signal of the encoder 14. The signal synchronizingcircuit 42 controls the system clock generation circuit 41 so that thereference clock or the reproduction clock is output.

[0041] The recording control circuit 21 controls the interrupt/restartcircuit 43. The interrupt/restart control circuit 43 controls theencoder 14 and the laser drive circuit 16 and, when the buffer underrundetermination circuit determines that the buffer memory 13 has entered astate in which buffer underrun may occur, provides the address memories47, 48 with a recording interrupt signal.

[0042] The address memory 47 stores the address of the read data in thebuffer memory 13 when receiving the recording interrupt signal from theinterrupt/restart circuit 43.

[0043] The address memory 48 stores the address of the ATIP decoded bythe ATIP decoding circuit 10 when receiving the recording interruptsignal from the interrupt/restart circuit 43.

[0044] When data is reproduced during a recording restart mode(described later), the location detection circuit 45 compares theaddress of the data read from the buffer memory 13 with the addressstored in the address memory 46. If the data address and the staredaddress are the same, the location detection circuit 45 activates therecording restarted signal.

[0045] When data is reproduced during the recording restart mode, thelocation detection circuit 46 compares the address of the ATIP decodedby the ATIP decoding circuit 10 with the ATIP address stored in theaddress memory 48. If the decoded ATIP address and the stored ATIPaddress are the same, the location detection circuit 46 activates therecording restart signal.

[0046] The retry determination circuit 44 instructs the recordingcontrol circuit 21 to restart the recording operation of the interface12, the access control circuit 19, and the system control circuit 22when the restart signals of the location detection circuits 45, 46 aresimultaneously activated. When the two restart signals are notsynchronously activated (when the restart signals are activated atdifferent timings), the retry determination circuit 44 instructs thecontrol circuit 21 to repeatedly perform data reproduction in therecording restart mode until the two restart signals are synchronouslyactivated.

[0047] The operation of the CD-R drive 1 will now be discussed.

[0048] When a user manipulates the personal computer 31 to record data,the personal computer 31 generates a command accordingly. The command istransferred to the recording control circuit 21 via the interface 12. Inresponse to the command, the recording control circuit 21 controls theinterface 12, the access control circuit 19, and the system controlcircuit 22 to record data.

[0049] When recording begins, the signal synchronizing circuit 42switches the operational clock output of the system clock generationcircuit 41 to the reference clock. As a result, the circuits 7-10, 12-6,19-22 of the CD-R drive 1 are synchronized with the operational clock,or the reference clock.

[0050] The data provided from the personal computer 31 is stored in thebuffer memory via the interface 12 and read from the buffer memory 13 insector units. The encoder 14 encodes the data read from the buffermemory 13 in sector units to generate recording data. The laser drivecircuit 16 provides the optical head 4 with drive signal having avoltage corresponding to the recording data. In accordance with thedrive signal, the optical head 4 changes the intensity of the laser beamirradiated against the optical disc 32. This forms recording pits on therecording layer of the optical disc 32 and records data on the opticaldisc 32. Simultaneously, from the laser beam reflected by the opticaldisc 32, the optical head 4 reproduces the data recorded on the opticaldisc 32 as the RF signal. The RF amplifier 5 amplifies the RF signalprovided from the optical head 4 to generate digital data. The wobbledecoder 9 extracts the wobble component from the digital data and usesthe wobble component to generate the rotation control signal. Inaccordance with the rotation control signal, the spindle servo circuit 3controls the spindle motor 2 so that the optical disc 32 is rotated at aconstant linear velocity. The ATIP decoding circuit 10 decodes the ATIPusing the wobble component and extracts the ATIP address of the absolutetime information in the ATIP.

[0051] When the transmission rate of the data provided from the personalcomputer 31 is slower than the transmission rate of the data recorded inthe optical disc 32 (write speed), that is, when the transmission rateof the data provided to the buffer 13 is slower than that of the dataoutput from the encoder 14, the amount of data stored in the buffermemory 13 decreases. When the buffer underrun determination circuit 20determines that a buffer underrun error may occur in the buffer memory13, the recording control circuit 21 controls the interrupt/restartcircuit 43 so that, before the occurrence of a buffer underrun in thebuffer memory 13, the address memories 47, 48 are accordingly providedwith the interrupt signal and the output of recording data from theencoder 14 is interrupted.

[0052] In this state, when the level of the recording data output fromthe encoder 14 goes low, the interrupt/restart circuit 43 outputs theinterrupt signal and stops the output of the recording data from theencoder 14. In response to the interrupt signal, the address memories47, 48 store the data address of the buffer memory 13. In other words,the address memory 47 stores the buffer memory address of the data readfrom the buffer memory 13 when receiving the interrupt signal. Theaddress memory 48 stores the ATIP address of the ATIP decoding circuit10 when receiving the interrupt signal.

[0053] When the output of the recording data from the encoder 14 isinterrupted, the transmission of the drive signal from the laser drivecircuit 16nto the optical head 4 is impeded. This stops the emission ofthe laser beam from the optical head 4 and interrupts the recording ofdata on the optical disc 32.

[0054] When the interrupt/restart circuit 43 outputs the interruptsignal, the sector of the data being output from the encoder 14 isrecorded on the optical disc 32. The interrupt signal of theinterrupt/restart circuit 43 may be output at times between sectors ofthe recording data.

[0055] Subsequent to the recording interruption, the data provided fromthe personal computer 31 is stored in the buffer memory 13 via theinterface 12. As the amount of data stored in the buffer memory 13increases, the state in which a buffer underrun may occur no longerexists. When the buffer underrun determination circuit 20 determinesthat buffer underrun is not likely to occur, the recording controlcircuit 21 controls the access control circuit 19 and the system controlcircuit 22 to perform data reproduction in the recording restart mode.

[0056] When data reproduction is performed in the recording restartmode, the access control circuit 19 controls the head servo circuit 6.The head servo circuit 6 controls focusing, tracking, and sled feed ofthe optical head 4 to move the optical head 4 to a sector location thatis prior by a predetermined number of sectors from the sector at whichthe recording interruption occurred. The optical head 4 then irradiatesthe laser beam from that sector location.

[0057] The interrupt/restart circuit 43 controls the laser drive circuit16 so that a drive signal having a constant voltage is output from thelaser drive circuit 16. This results in the optical head 4 irradiatingthe optical disc 32 with a relatively weak laser beam. The reflectedlaser beam reproduces the data recorded on the optical disc prior to therecording interruption, and the optical head 4 outputs the RF signal.The RF signal is amplified by the RF amplifier 5 and converted todigital data. The decoder 7 decodes the digital data, extracts a pitclock from the digital data, and separates a subcode from the digitaldata. A subcode synchronizing signal is generated from the subcode. Thesubcode is decoded by the subcode decoding circuit 8 to generate thesub-Q data.

[0058] When data reproduction in the recording restart mode is started,the signal synchronizing circuit 42 switches the operational clock fromthe reference clock of the crystal oscillation circuit 18 to thereproduction clock of the decoder 7. The circuits 7-10, 12-16, 19-22 ofthe CD-R drive 1 are operated in accordance with the reproduction clock.By using the reproduction clock, the data recorded on the optical disc32 prior to the recording interruption is accurately reproduced.

[0059] The recording control circuit 21 controls the interrupt/restartcircuit 32 to instruct the encoder 14 to restart the output of therecording data. The encoder 14 goes back by a predetermined number ofsectors from the data address of the buffer memory 12 at which therecording interruption occurred and starts reading data in sector unitsfrom that sector of the buffer memory 13. The encoder 14 adds a synchbyte, a header, an ED, and an ECC to the read data, performs the CIRCand EFM processes, and adds a subcode, which includes the sub-Q data,and the subcode synchronizing signal to the read data.

[0060] The drive signal of the laser drive circuit 16 is constant duringdata reproduction in the recording restart mode. In other words, thedrive signal of the laser drive circuit 16 has a low voltage.Accordingly, laser irradiation does not affect the data recorded on theoptical disc prior to the interruption.

[0061] The signal synchronizing circuit 42 controls the access controlcircuit 19 via the recording control circuit 21 and synchronizes thedata recorded on the optical disc 32 with the recording data output fromthe encoder 14. In other words, the signal synchronizing circuit 42controls the recording control circuit 21 and the access control circuit19 so that the subcode synchronizing signal of the decoder 7 issynchronized with the subcode synchronizing signal of the encoder 14 andthe sub-Q data of the subcode decoding circuit 8 is associated with thesub-Q data of the encoder 14.

[0062] The location detection circuit 45 compares the address of thedata read from the buffer memory 13 with the address stored in theaddress memory 47 and activates the restart signal when the data addressand the stored address are the same. The address stored in the addressmemory 47 is the address of the data read from the buffer memory 13 whenthe recording of data is interrupted.

[0063] The location detection circuit 46 compares the ATIP address ofthe ATIP decoding circuit 10 with the ATIP address stored in the addressmemory 48 and activates the restart signal when the ATIP address and thestored address are the same. The ATIP address stored in the addressmemory 48 is the ATIP address decoded by the ATIP decoding circuit 10when the recording of data is interrupted.

[0064] When the restart signals of the location detection circuits 45,46 are simultaneously activated, the retry determination circuitcontrols the interface 12, the access control circuit 19, and the systemcontrol circuit 22 via the recording control circuit 21. The signalsynchronizing circuit 42 switches the operational clock of the systemclock generation circuit 41 from the reproduction clock to the referenceclock when recording is restarted.

[0065] Upon the restart of the recording, the address of the data readfrom the buffer memory 13 shifts to the address next to the address atwhich data recording was interrupted. Further, the address memory 48 andthe location detection circuit 46 shift the sector location of theoptical disc 32 irradiated by the laser beam to the sector location nextto the sector location at which data recording was interrupted. In thisstate, the signal synchronizing circuit 42 synchronizes the recordingdata output from the encoder 14 with the data recorded on the opticaldisc 32. Accordingly, the data of the sector next to the sector at whichdata recording was interrupted is recorded upon the restart of therecording. In other words, sectors of data are recorded without anyinterruptions when restarting recording. This ensures the continuity ofthe recorded data awhile preventing the occurrence of a buffer underrunerror.

[0066] As described above, when the level of the recording data outputfrom the encoder 14 goes low, the interrupt/restart circuit 43 outputsthe interrupt signal and stops the output of the recording data from theencoder 14. Thus, when the recording operation is restarted, therecording data output from the encoder 14 is low, and the laser drivecircuit 16 outputs a drive signal, the level of which is the same asthat when data is reproduced. Accordingly, the power of the laser beamemitted from the optical head 4 is relatively low. That is, the laserbeam power of the optical head 4 is low when restarting the recordingoperation at the same data recording location. Therefore, data that hasalready been recorded is not damaged even if the recording restartlocation is offset from where it should be. Further, since the laserbeam is not emitted against the recording section corresponding to thelow level data, the diameters of pits do not become non-uniform.

[0067] For example, if the high level of the recording data were outputfrom the encoder 14, the drive signal output but the laser drive circuit16 would have a voltage level that is several tens of times greater thanwhen data is reproduced. Thus, the power of the laser beam output fromthe optical head 4 would be several tens of times greater than thatduring the data reproduction operation. However, it is difficult toinstantaneously activate the laser power of the optical head 4 toseveral tens of times greater than that during the data reproduction. Todo so, a certain time period would be necessary. Thus, it would taketime to increase the laser power to a desired level when activating theoptical head 4 simultaneously with restarting the recording operation.Such delay would form a non-recording section on the optical disc 32 andproduce an interruption in the recording data.

[0068] Further, when restarting the recording operation, if the opticalhead 4 emits the laser beam against the wrong data sector of the opticaldisc 32, data may be rewritten to a sector on which data has alreadybeen recorded. In such case, if a high power laser beam is emittedagainst a recording layer of the optical head 32 at which recording pitshave already been formed, the recording pits may be enlarged and mayoverlap with recording pits of other sectors or tracks. Consequently,data would not be recorded correctly. Further, if the timing of therecording restart is delayed, data is not recorded at the recordingrestart position. This may divide a pit into two and record erroneousdata. Even if the location where the recording is restarted exactlymatches the location where the interruption occurred, the power of thelaser beam prior to the interruption differs slightly from thesubsequent to the restart. This would cause the recording pits at therecording restart position to have non-uniform sizes that result in dataread errors.

[0069] In the preferred embodiment, the recording operation isinterrupted at a time at which the level of the recording data outputfrom the encoder 14 goes low. Thus, the power of the laser beam outputfrom the optical head 4 is low when the recording operation isrestarted. As a result, the above-described problems do not occur.

[0070] The optimal time for interrupting the writing of data is at theoutput of synch pattern data located to the head of each sector. In theCD standards, a synch pattern has 24 bits and includes 11 high bits and11 low bits. In other words, the head of each sector includes a periodof 11 consecutive low bits, which is the longest low period in the CDstandards. An address is designated for each sector. Thus, the addressmemories 47, 48 hold address data corresponding to sector addresses.Accordingly, the optimal time for interrupting data writing would beduring the synch pattern of a sector. By interrupting the writing ofdata in this manner, it is not necessary to activate the laser power ofthe optical head 4 when restarting the recording operation and theformation of abnormal recording pits due to the rewriting of recordingdata is prevented.

[0071] It is preferred that the buffer underrun determination circuit 20determine that there is a possibility of a buffer underrun occurringwhen at least one sector of data is still in the buffer memory 13.

[0072] When the two restart signals of the location detection circuits45, 46 are not synchronously activated (when the two restart signals areactivated at different times), the retry determination circuit 4repeatedly performs data reproduction in the recording restart moreuntil the two restart signals are synchronously activated. In otherwords, if an external disturbance occurs for one reason or another(e.g., the application of an external impact to the CD-R drive), theelements 2-22 of the CD-R drive 1 may function erroneously such that thetwo restart signals are not synchronously activated. Thus, the retrydetermination circuit 44 repeats data reproductions to avoid theinfluence of an external disturbance. If the restart signals of theposition detection circuits 45, 46 are simultaneously activated, theretry determination circuit 44, the position detection circuit 45, andthe address memory 47 may be deleted.

[0073]FIG. 2(A) is a schematic view showing a sector of the optical disc32. FIG. 2(b) is a diagram illustrating the addresses of the buffermemory 13. Sectors Sn+1, Sn, Sn−1, Sn−2, . . . , Sn−m shown in FIG. 2(a)are respectively associated with addresses An+1, An, An−1, An−2, . . . ,An−m shown in FIG. 2(b).

[0074] During recording, data is read from the buffer memory 13 in theorder of addresses An−m, . . . , An−2, An−1, An, and the recording dataencoded by the encoder 14 is recorded on the optical disc 32 in theorder of sectors Sn−m, . . . , Sn−2, Sn−1, Sn. For example, if thebuffer underrun determination circuit 20 determines during the recordingof data that a bus underrun may occur at address An, the data of sectorSn, which is associated with address An, is recorded. However, therecording of data is interrupted from the sector Sn+1, which isassociated with address An+1.

[0075] When the recording of data is interrupted, address An is storedin the address memory 47, and the address of the ATIP decoded from thedata recorded at sector Sn is stored in the address memory 48.Afterward, when the buffer underrun determination circuit 20 determinesthat a buffer underrun is no longer likely to occur, data reproductionin the recording restart mode is commenced from sector Sn−m by goingback from sector Sn, at which recording was interrupted, by apredetermined number of sectors (in this case, m sectors).

[0076] When data reproduction is commenced, data is read from the buffermemory 13 from address An−m by going back from address An, at whichrecording was interrupted, by a predetermined number of addresses (maddresses). The read data is encoded into recording data by the encoder14.

[0077] The signal synchronizing circuit 42 synchronizes the recordingdata output from the encoder 14 with the data recorded on the sectorsSn−m to Sn of the optical disc 32. Then, when the address of the dataread from the buffer memory 13 matches the address An stored in theaddress memory 47, the restart signal of the location detection circuit45 is activated. When the address of the ATIP decoded by the ATIPdecoding circuit 10 matches the ATIP address of the sector Sn stored inthe address memory 48, the restart signal of the location detectioncircuit 46 is activated. When the two restart signals of the locationdetection circuits 45, 46 are simultaneously activated, the retrydetermination circuit 44 restarts the recording of data from sectorSn+1, which is next to the sector Sn at which data recording wasinterrupted.

[0078] It is preferred that the predetermined sector number (m sectors)be sufficient for obtaining time period T1, which is required for thespindle serve circuit 3 to control the spindle motor 2 and the headservo circuit 6 to control the optical head 4, and time period T2, whichis required for synchronization by the signal synchronizing circuit 42.For example, m is set at 10 to 30. The time periods T1, T2 increase asthe recording speed of the CD-R drive 1 becomes higher, for example, asthe recording speed increases from 4× to 8×. Accordingly, it ispreferred that the predetermined sector number be increased as therecording speed increases.

[0079] In the present invention, the recording operation is interruptedwhen the power level of the laser beam becomes low or during the periodwhen the power of the emitted laser beam is low. This prevents theformation of non-uniform recording pits at the recording restartlocation. Thus, abnormal recording pits are not formed due to therewriting of data.

[0080] The recording operation is interrupted when the power level ofthe laser beam is low and the synch pattern data of the 11 consecutive,low level bits is output. Further, the address of the sector at whichthe recording interruption occurred is stored in the address memories.Accordingly, the synch pattern and the sector address facilitate therestart of data recording.

[0081] It should be apparent to those skilled in the art that thepresent invention may be embodied in many other specific forms withoutdeparting from the spirit or scope of the invention. Particularly, itshould be understood that the present invention may be embodied in thefollowing forms.

[0082] (1) The present invention may be applied to a data recorderemploying the constant angular velocity (CAV) component, which isextracted by the wobble decoder 9, is generated and used as theoperational clock during the recording of data.

[0083] (2) The access control circuit 19, the bugger underrundetermination circuit 20, the recording control circuit 21, and thesystem control circuit 22 may be replaced by a microcomputer thatincludes a CPU, a ROM, and a RAM. In other words, the function of eachcircuit may be achieved by having a microcomputer perform variousoperations.

[0084] (3) The present invention may be applied to a data recorder(e.g., CD-RW drive, MD drive) that uses a rewriteable recording medium(e.g., CD-RW standard optical disc, MD standard optical disc). In suchcase, the occurrence of a buffer underrun error is prevented. Thisdecreases the time required for the recording of data.

[0085] The present examples and embodiments are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given herein, but may be modified within the scope andequivalence of the appended claims.

What is claimed is:
 1. A controller employed in a data recorder tocontrol interruption and restart of recording data, wherein the datarecorder records on a recording medium data stored in a buffer memory byemitting a laser beam against the recording medium, the laser beam beinggenerated at a high level and a low level, wherein the laser beam at therelatively high power level forms a recording pit on a recording layerof the recording medium and the laser beam at the relatively low leveldoes not form a recording pit on the recording layer of the recordingmedium, the controller comprising: a buffer underrun determinationcircuit for determining whether or not the buffer memory is in a statein which buffer underrun may occur based on the amount of data stored inthe buffer memory; an address memory for storing at least one of anaddress of the recording medium and an address of the buffer memory whendata recording on the recording medium is interrupted, each addressindicating a location of data when the recording interruption occurred;a synchronizing circuit for sequentially reading the data recorded onthe recording medium prior to the recording interruption and the datastored in the buffer memory prior to the recording interruption andsynchronizing the recorded data and the stored data based on asynchronizing signal of a subcode; restart circuitry for restarting datarecording on the recording medium based on the address stored in theaddress memory and; interrupt control circuitry for interrupting datarecording if the laser beam is generated at the relatively low powerlevel when the buffer underrun determination circuit determines that theamount of data in the buffer memory may become null and cause the buffermemory to become empty.
 2. The controller according to claim 2, whereinthe data includes synch pattern data, the laser beam is generated at therelatively low power level and the relatively high power level inaccordance with the synch pattern data, and the interrupt controlcircuit interrupts data recording when the laser beam is generated atthe relatively low power level in accordance with the synch patterndata.
 3. The controller according to claim 2, wherein the data isrecorded in the recording medium in sector units, each sector includingsector address data, and wherein the address memory stores the sectoraddress data where the recording interruption occurred.
 4. A controllerfor a data recorder, wherein the data recorder records data on arecording medium by emitting a laser beam against the recording medium,the controller comprising: a buffer underrun determination circuit fordetermining whether or not the buffer memory is in a state in whichbuffer underrun may occur based on the amount of data stored in thebuffer memory; a laser drive circuit, which controls the power level ofthe laser beam; and an interrupt control circuit for continuingrecording when the buffer memory is in a state in which buffer underrunmay occur and interrupting the recording operation when the laser beamis generated at the low power level.
 5. A method for interrupting datarecording in a data recorder to prevent the occurrence of a bufferunderrun error, wherein the data recorder records data on a recordingmedium by emitting a laser beam against the recording medium, the methodcomprising: determining whether or not a buffer memory of the datarecorder is in a state in which buffer underrun may occur based on theamount of data stored in the buffer memory; continuing recording when apredetermined state is detached; and interrupting the recordingoperation when the buffer memory is in a state in which buffer underrunmay occur and the laser beam is generated at the low power level.
 6. Amethod for interrupting and restarting data recording in a data recorderto prevent the occurrence of a buffer underrun error, wherein the datarecorder records on a recording medium data stored in a buffer memory byemitting a laser beam against the recording medium, the methodcomprising: determining whether or not the buffer memory is in a statein which buffer underrun may occur based on the amount of data stored inthe buffer memory; interrupting data recording if the laser beam isgenerated at a low power level when the buffer memory is in the state inwhich buffer underrun may occur; storing in an address memory an addressof the recording medium when data recording on the recording medium isinterrupted, the address indicating a location of data when therecording interruption occurred; sequentially reading the data recordedon the recording in medium prior to the recording interruption; andrestarting data recording on the recording medium based on the addressstored in the address memory.